Balance testing appliance



Nov. 1, 1949 l. A. WEAVER ET AL 2,437,035

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BALANCE TESTING APPLIANCE Filed July 20, 1945 7 Sheets-Sheet 6 Nov. 1, 1949 x. A. WEAVER ETAL BALANCE TESTING APPLIANCE '7 Sheets-Sheet '7 Filed July 20, 1945 INVENTOR-S J70 Q. Meaz/efl Patented Nov. 1, 1949 BALANCE TESTING APPLIANCE Ira A. Weaver and Clyde H. Phelps, Springfield,

ors, by mesne assignments, to Weaver Engineering Co., a corporation of Illinois Application July 20, 1945, Serial No. 606,050

22 Claims. (CI. 73-66) This invention concerns certain valuable betterments in balance testing machines such as are used to determine the amount and location of unbalance in a suitably supported revolving rotor whereby the latter is tested as to its dynamic equilibrium and the degree of the latter is indicated by suitable means. The invention is useful to analyze the unbalance of similar rotors so that suitable corrective steps may be taken to bring them to dynamic balance.

An object of the invention is to provide an appliance of this kind which is relatively simple in structure, which is reliable in results, which is of comparatively low cost, which is unlikely to become damaged or injured in ordinary service and which is easily operated.

In order to understand the invention, it is well to deal initially with some fundamental elemental balancing principles and that course will be followed.

In the drawings, forming a part of this specification, and to which reference should be had in connection with the succeeding description:

Figures 1 to 23 inclusive present various diagrams;

Figure 24 is a longitudinal section through one of the crystal electric generators;

Figure 25 is a lengthwise section thereof on line 2525 of Figure 24;

Figure 26 shows the electric circuits in which such generators are used;

Figure 27 is a front elevation of the balance testing machine;

Figure 28 is a plan view of the same machine;

Figure 29 is an end elevation of the machine;

Figure 30 is a fragmentary view of a slightly modified machine; and

Figure 31 is a partial end view of the machine of Figure 30.

By reference to these drawings, it will be noted that Figure 1 represents a disc the shaft of which is mounted on two, parallel, horizontal, v bars or rails 52, 52, this disc being in complete balance except that a weight 53.has been attached to the rim thereof, as illustrated, causing the disc to roll on the rails by reason of the fact that the weight seeks its lowermost position, as shown.

As indicated, in Figure 2, another weight 54 of the same value has been attached to the disc in the same plane and diametrically opposite weight 53 to bring the disc to complete static balance, thereby removing its tendency to roll.

Figures 3 and 4 portray a cylinder 55, similarly mounted and in complete static balance, as the two weights 55 and 51 are of equal value and at- 2 tached to the perfectly balanced cylinder in the same plane though offset longitudinally of the cylinder, but upon rotation the cylinder is not in dynamic balance.

Figures 5 and 6 present the same cylinder and weight combination as in Figures 3 and 4 and upon rotation of such cylinder, if the latter is freely suspended, the two weights will cause the ends of the cylinder to oscillate in opposite directions. and because the centrifugal force of weight 56 in the direction of its arrow is the opposite of that of weight 51 in the direction of its arrow, the cylinder is diametrically unbalanced.

However, if weight 51 be removed and attached to the cylinder at point 50 in the transverse plane of weight 56 complete balance will be obtained.

Figures 7, 8 and 9 illustrate the same cylinder 55 fitted with unbalance weight 56 corrected byweight 51 opposite and in the same plane and an unbalance weight 58 corrected by weight 59 in the same plane, this cylinder,therefore, being in complete balance both statically and dynamically.

Figure 10 represents the same cylinder 55 with transverse correction planes selected at I00 and NH, but the unbalance weight BI is not in either correction plane and, therefore, if the two weights, 62 in correction plane I 00, and B3 in correction plane HH, whose sum is equal to that of weight 6|, were removed and a weight equal to that of weight 6| were attached 180 degrees around the cylinder from weight 6| and in either correction plane, static balance would be obtained but dynamic unbalance would be created. With relation to such statically balanced cylinder, weight 62 multiplied by the distance b equals weight 63 multiplied by the distance 0 and consequently the forces are in balance opposite weight 6| and the cylinder is in complete balance.

Figures 11, i2, 13, 14 and 15 show the same cylinder as presented in Figure 10 with the weight 6| balanced by the weights 82 and 63 in the two correction planes I00 and l0l and with another unbalance weight 64 balanced by two additional weights 65 and 66 also in the two correction planes I00 and NH. The two correction weights 62 and 66 in correction plane I00 may be replaced by a single weight of resultant value located at position 61 as indicated in Figure 13 and the correction weights 63 and '65 in correction plane Hll may be replaced by a single weight of resultant value located at position 68 in correction plane I0! and then the cylinder would be in coplee balance.

It follows from the foregoing that any rigid rotor may be brought to complete balance (both static and dynamic) by mass correction in any two or more selected planes of correction.

If a balancing machine be provided that will indicate the value and position of unbalance in each of two or more selected planes of correction without efiect from unbalance in any other plane, complete balance can be obtained, such a machine indicating the resultant value of positions El and 68 in Figures 13 and 15.

Accordingly, the present invention relates to balance testing machines of the type arranged to indicate the unbalance in predetermined planes of correction.

Balance testing machines in general have been based upon a flexible mounting to support the rotor for rotation with freedom to vibrate in at least one plane, usually the horizontal, in order that the oscillation caused by the unbalance may be indicated.

Some balance testing machines have been provided with means to pivot the rotor efiectively at one selected correction plane in order to indicate unbalance in another selected plane of correction whereby the unbalanced forces in the plane of the pivot are directed to the pivot and are without efi'ect at another correction plane, but, as the pivot is a stationary part of the frame or mounting, undesirable vibrations are transmitted to the frame causing unreliable indications, as the indicating means are a part of the stationary mounting or frame structure.

Another type of balance testing machine employing a similar flexible mounting means but without the use of a fixed pivot, uses a complex mathematical electrical net-work designed to receive electrical impulses from two generators, operable from each bearing. The two electrical impulses are fed to the complicated electrical network which is intended to so combine th impulses received as to give a result in proportion to the unbalance in one correction plane. These generator indicator devices are operable from the motion at the bearings, but are mounted on the frame structure and are, accordingly, subject to objectionable vibrations which may cause inaccurate indications.

Other types of balance testing machines are founded upon a mounting similar to the above,

but employing mechanical systems designed to counterbalance the vibration caused by unbalance through counterbalancing mass systems variable in value and angular relation.

The present invention involves the use of freely suspended bearing supports for the rotor arranged so that the rotor may vibrate or oscillate unrestrictcdly in the horizontal plane, these bearing supports being arranged for attachment thereto of relatively small, variable mass systems designed to take up vibration similar to that of the rotor, but adjustable to respond to vibrations caused by unbalance in one correction plane of the rotor without effect of unbalance in another plane. The comparatively small variable mass system is a part of the rotor and bearing support and all are free to move as a unit in space and it, therefore, comprises a pendulum suspended seismic mass substantially free from floor or building vibrations.

The variable mass system may be adjusted to respond to the unbalance in any selected plane of correction, and, therefore, one such system may be employed to respond to each of several chosen planes of correction by adjustment of the variable mass system for each plane selected.

For convenience, however, one variable mass system is, or more variable mass systems are, attached to each bearing support and each adjusted for response to the unbalance in one selected plane of correction whereby each such system is independent of the others.

An outstanding important object of the invention is the provision of mechanical physical means to permit the accurate indication of the position and value of unbalance in one correction -plane without efiect from unbalance in another plane.

Another aim of the invention is to supply a sys= tem with which the testing may be accomplished over a wide speed range in order that rotors may be tested as to balance at a speed at which they normally run in service.

The basis of this invention involves the application of inertia forces set up in the rotor by reason of the unbalance in the planes selected for correction.

In Figure 16 a rotor ii is shown with bearings at E2 and 13 with one correction plane selected at E5 in which unbalance it has been attached, the rotor otherwise being in perfect balance and suspended on long, thin wires ll, attached to the bearings so that upon rotation, due to the unbalance IE, the rotor will vibrate or oscillate in the horizontal plane through which it has complete freedom of movement.

The same rotor, in a diiferent angular position, is presented in plan view in Figure 17 with the unbalance 76 in the correction plane 75, the horizontal movement of the geometrical center line of the rotor caused by the unbalance it, being indicated at 18, and because of the mass distribution or inertia quality of the rotor, the unbalance it causes such geometrical center line to move in the direction of and to the position 8! at the left hand end and in the direction of and to the position 82 at the right hand end. Therefore, the motions at bearing l2 and bearing 13 have a phase difierence of 180 degrees, and also at any point of minimum or maximum amplitude of oscillation, the motions of bearings 12 and 13 are in opposite directions or 180 degrees phase difference. However, both bearing 12 and 13 have motion due to the single unbalance present in the correction plane 75. It follows, therefore, that any indication of amplitude of oscillation taken at bearing 73 would include component 83 due to unbalance 16 in plane 15, and this component 83 is acting in the opposite direction or 180 degrees from the opposite end of the rotor as at 8|.

Hence, it is manifest that the component 83 must be eliminated or removed from the indication taken at bearing 13 before a true indication of the unbalance at the correction plane 85 is made.

By reference to Figure 18, the same rotor H is again present, excepting that the balance 16 has been removed from correction plane 15 and attached to the rotor in correction plane 85, unbalance 16 now causing oscillation amplitude 86 at the right hand end, and amplitude 81 at the left hand end, and, as before, the motions at bearing 12 and at bearing 13 are in opposite directions or have a phase diflerence of degrees. Consequently, any indication taken at bearing 12 will include component 88 due to unbalance 76 in correction plane 85. Clearly, then, component 88 must be removed or eliminated from any indication taken at bearing 72 before a correct indication of the unbalance at correction plane 15 is made.

Turning now to Figure 19, a rotor 9| with different inertia properties is shown with the unbalance I8 attached thereto in correction plane 85 causing the amplitude of motion 92 at the right hand end and the amplitude 93 at the left hand end, the different inertia quality of this rotor having caused the intersection of .the lines of motion to occur at a point to the left of bearing I2. Consequently, the motions of bearings 12 and I3 are in phase with one another as both bearings are moving in the same direction at all times and component 94 at bearing 12 due to the unbalance in plane 85 is in phase with the motion at bearing I3.

As a result, component 9| must be excluded or banished from any indication taken at 12 before a correct indication of the unbalance at the left hand correction plane I is made.

From the foregoing it will be appreciated that the motions at bearings 12 and I3, due to the unbalance in one correction plane, may be either in or out of phase, depending upon the inertia characteristics of the revolving rotor undergoing test. 1

Turning now to Figure 20, wherein is shown a rotor 99 of still different inertia quality and where the unbalance I6 is attached in the correction plane 85 causing the amplitude of motion 95 at the right hand end but zero motion at bearing 12, the indications taken at point 98 of bearing I2 would not contain any component due to unbalance I6 in plane 85 but would provide reliable indication of unbalance in another correction plane, such as plane 15.

The illustration in Figure 21 is the same as that in Figure 20 except that unbalance I6 has been removed from correction plane 85 and attached to the rotor in correction plane I5 causing the amplitude of motion 91 at the left hand end but zero motion of the bearing I3, so that indications taken at point 98 of bearing I3 would not contain any component due to unbalance 16 in plane 15 and would provide reliable indications of unbalance in another correction plane, such as plane 85.

It is, therefore/apparent that the motions at bearings 12 and. 13, due to unbalance in one plane, may be in phase or out of phase or one hearing may have zero motion.

The current invention provides a mass system adapted for attachment to the balance-indicating machine in a manner such that it becomes part of the pendulum rotor bearing and hanger ystem and is, therefore, seismic-mounted and inertia-operated and will vibrate or oscillate in phase with the point of attachment.

Referring to Figure 22, there is shown therein a rotor I02 with unbalance I03 inserted in correction plane 15, this unbalance causing the geometric center line I 04 of the rotor to have to position I05 which is the position of maximum amplitude of oscillation in the direction shown.

Points I06 and III! are 180 out of phase, but points I 08 and I09 are exactly in phase, point I09 having attained greater velocity than point I08 in order to reach its maximum amplitude at the same time that point I08 reaches its smaller maximum amplitude.

In Figure 23, the mass I I0 and the smaller mass II I, shown as mounted on a common axis II2 pivoted for rotary movement about the point I I3 along the geometric axis or center line II4 of the rotor, have been added to the structure presented in Figure 22, these two masses I I0 and I I I having individual adjustment on their common axis 2 along the geometric center line I of the rotor.

If the mass III having a higher velocity than that of the mass I Ill be adjusted along such common axis II2 toward or away from the heavier mass IIO having a lower velocity, a point of adjustment between the two masses may be found where the inertia of the smaller mass of higher velocity will equal the inertia of the larger mass of lower velocity such that zero torque would be applied about pivot II3 during the vibration or oscillation of the rotor and the two-mass axis I I2 would remain parallel to the geometric center line, prolonged, of the rotor, and therefore the unbalance I03 would have zero torque effect about pivot II3.

It follows that any indicator operable from movement of the two masses about pivot H3 would provide a zero reading for any unbalance in correction plane 15 but would indicate unbalance in any other transverse plane along the geometric axis of the rotor and that the motion about pivot I I3 would be in phase with, and proportional to, any unbalance in any other transverse plane, except plane I5.

The two masses I I0 and II I adjustably mounted lengthwise on a common axis II2 can be piv otally attached to either bearing I2 or bearing I3 illustrated in the foregoing figures of the drawings and adjusted to provide zero motion about pivot II3 for any unbalance in a selected correction plane whether the motions or vibrations at the bearings are in phase or out of phase, or have zero motion at the bearings.

It is further clear in the case of zero motion at the bearing as in Figure 20 or Figure 21 that one mass only, either III) or III would be required and that one positioned at point 96 of Figure 20 or 98 in Figure 21.

This mass system III], III, H2, H3 then provides means to indicate, through the motion about the pivot II 3 of Figure 23 the value of the unbalance in a selected plane of correction and its angular position or point of unbalance, without effect from unbalance in any other plane.

In the actual full size balance indicating appliance described in detail below, the rocking or vibration of this two mass system about the axis H3 is employed for operation of a piezoelectric crystal generating element some of the details of which do not of themselves constitute a part of this invention since such an appliance is known.

Referring to Figures 24 and 25, the two weights or masses H0 and III have screw threaded connections with the straight shaft or rod I I2 so that they can be individually adjusted lengthwise thereon, each such weight having a set-screw II8 for maintaining it in its adjusted position. This shaft II2 extends through a transverse screw-threaded hole in the head I I I of a spindle II 8, a set-screw II9 holding the part II2 fixedly in its adjusted position in such head and at a right angle to the axis of the spindle. Spindle -II8 fits inside of a metal member I2I (Fig. 25)

in which it is demountably retained by an accessible set-screw I22, equipped with a knurled head I23, extending into a longitudinally divided housint. I24.

Member I2I has two, oppositely extended, cylindrical portions I25 and I26 oscillatory respectively in rubber bearings I21 and I28 in the housing.

The two sections of the casing I24 are normally held together in assembled relation as illustrated by four, hollow rivets I29, I29 by means of which the whole appliance may be readily mounted in proper position, as by screws, not shown, extended through the rivets.

The inner end of part I26 is provided with a clamp I3I fitting over the corresponding end of the fiat crystal generator I 32 consisting of a pair of thin, rectangular crystals of Rochelle salt, tourmaline, quartz, or other comparable minerals joined together in known manner, the opposite end of the crystals having wires I33 connected thereto and provided with corresponding external terminals I34, I34, such end portion of the crystals being held between fixed rubber or other comparable elastic pads I35, I35, the construction being such that, when the spindle H8 is turned in either direction from its normal neutral position, the crystals are twisted and strained and by reason of which action they create a minor electric voltage and, as soon as the strain or twist is removed, the crystals automatically return to normal position by reason of the reflex action of the pads I35, I35, the crystals and the spindle being held in this neutral position by the friction of the rubber bearings I21, I28.

The balance testing machine, as presented in Figures 2'1, 28 and 29 includes a suitable base [M with end standards I43, I43, of the shape depicted in Figure 29 and open at the front at I42 and each supporting a pair of depending wires I44, I44 which at their lower ends support a bearing member I45 rotatably supporting the shaft I46 of the rotor I41 to be tested as to its balance, such rotor being revolved by a belt I48 encircling it and driven by a suitable electric motor I49 on the base I4I.

Each such bearing member I45 has a depending portion II on the lower end of which is mounted one of the two-weight crystal generating members designated as a whole I52 of the type and style presented in Figures 24 and 25, the terminals I34 of which are connected by wires I53 to electric terminals I54 on the standard I43.

A numerically graduated band I55 temporarily encircles and rotates with the rotor I41 and cooperates with the stroboscope lamp I56 and its associated fixed pointer or index I51 or known construction and operation.

Referring to Figure 26, it will be noted that the two terminals I54, I54 of one of the crystal devices I52 are connected to two electric contacts I6I, I6I and the corresponding terminals I54, I54 of the other crystal generator are connected to the other two terminals I62, I62 of a doublepole double-throw electric switch, characterized as a whole I63, whose terminals are joined to a second like switch I64 which may connect with a vacuum tube voltmeter I65 or with the stroboscope control amplifier I66 operatively associated with the stroboscope-lamp I56, whereby either crystal generator may be operatively connected to the voltmeter or to the stroboscope lamp.

Preliminary to the testing of the unknown unbalance characteristics of the rotor I41, a like rotor is balanced by trial and error, after which a known unbalance weight is affixed thereto in the left hand correction plane I15, as illustrated in Figure 27, and, during the rotation of the rotor, the two weights IIU and III of the mass system I52 on the right hand bearing member I45 are adjusted longitudinally with respect to one another on their common rod IIZ to eliminate all oscillation thereof about the axis II3 (Fig. 23) of the spindle II8 (Figs. 24 and 25) resulting in zero indication on the associated meter I65 and, after this condition has been established, such right hand mass assembly will respond to unbalance present in all transverse planes of the rotor except that in the left hand correction plane I15.

When the meter gives a zero reading as set forth above, the inertia values of the weights of difierent amounts are equal and there is, therefore, no tendency to twist the crystals.

When the meter indicates a value of unbalance, it is due to the fact that the two inertia forces of the two masses III] and III are not the same and do not balance one another.

Then this unbalance weight may now be removed from correction plane I15 and appliedto -the rotor in the right hand correction plane I85 (Fig. 2'7) and the mass assembly at the left hand end of the machine adjusted to zero response due to such applied weight and this left hand mass assembly will now respond to unbalance in any plane except the right hand correction plane I85.

Now the right hand mass assembly will respond and twist its crystals proportionately to any-unbalance attached in the right hand correction plane I85 and the left hand mass assembly will respond proportionately to any unbalance weight attached in the left hand correction plane I15, and, therefore, the indicating device I65 may be calibrated by the use of clifierent amounts of unbalance weights to read the response of the mass system to the unbalance in either of the two selected planes I15 and I85.

Thereupon, similar or comparable rotors of unknown unbalance properties may be tested without further mass system adjustment, the volt-meter I65 giving values of unbalance, and the stroboscope lamp and its cooperating graduated band and index giving angular positions values in these planes exact balance may be readily and quickly procured.

It may be noted that, when either bearing and its associated tester I52 moves in one direction from its normal neutral position and back again to that position, it creates-electric current, by

twisting of the crystals, in one direction which increases to a maximum and then back again to zero, and when it moves from its neutral position in the opposite direction and then back again to that position, it develops an opposite current up to maximum and then back to zero value. This device I52 constitutes a form of electric pickup sensitive to oscillatory motion of the rod I I2 with spindle II8.

In Figures 30 and 31, a balance testing machine using somewhat difierent shaped bearing mem-' bers I61 are shown, one only of these being illustrated. In this case such member has a forwardly extended, depending arm I58 on the front end of which the crystal generator I52 is mounted rendering the weights III] and III in more favorable position formanual adjustment, but the construction operates precisely as does the other one.

Those acquainted with this art will readily understand that the invention, as defined in the appended claims, is not necessarily limited and restricted to the precise and exact details illustrated and described and that reasonable modifications may be resorted to without departure from the heart and essence of the invention and without theloss or sacrifice oi any of its maject to the same angular motion as the geometric longitudinal axis of the rotor, such as the position shown in Figure 23, where the invention is pictured far to the right of the rotor bearing and that of Figure 29 where the horizontal longitudinal axis 01' screw H2, Figure 24, lies in the plane parallel to the horizontal longitudinal axis of the rotor.

Further, the mass I III and-the mass l H need not be of unequal weight or size as they may be identical and any desired ratio secured by ad- Justing the screw H2 through the stem nut H1 providing a longer or shorter lever arm about the axis of the member H8 for either mass.

We claim:

1. Designed to coact with a machine of known type adapted to support and to rotate horizontally on its axis a rotor to be tested with freedom for lateral, substantially horizontal vibration of the rotor due to its unbalance during such rotation. a balance testing system incorporating the combination of a piezoelectric crystal generator incl ding a vertical axis pivot having means operating said generator by turning of the pivot on its axis, means mounting said pivot on said machine in a manner to subject such ivot to said lateral vibration of the rota ing rotor. a longitudinal horizontal support fixed to said pivot and extending on opposite sides of said pivot parallel to the geometric axis 01' said rotor when such support is in its normal, neutral position, a pair of inertia weights adiustably mounted on said support on opposite sides of said pivot axis and manually adjustable longitudinally on said support toward and from one another, an electric circuit connected to said piezoelec ric crystal generator, and an electric meter usable in said circuit to which the voltage created by said generator is conducted and by which it is indicated, whereby said inertia weights may be initially adjusted relative to one another to cause zero reading by said electric meter for unbalance oi the revolving rotor in a selected transverse correction plane of the rotor and may be preliminarily calibrated by the employment of known weight means applied to the rotor to show the amount or unbalance in the rotor in another selected transverse correction plane of the rotor.

2. The balance testing system presented in claim 1, in which the rotor in said machine is supplied with a graduated band around it, with a stroboscopic lamp cooperating with said band, an electric circuit to supply said lamp with electric current, and means to connect said lamp circuit with the piezoelectric crystal generator whereby to permit determination of the angular position of the unbalance of the rotor in said other selected transverse correction-plane of the rotor.

3. The balance testing system presented in claim 1, in which said support for said weights on said pivot is a screw threaded rod with which screw threads on said weights permit adjustment of said weights along the rod.

4. The balance testing system set forth in claim 1, in which said weights are of difierent values, and in which said means supporting said weights along such rod.

on said pivot is a screw threaded rod with which screw threads on said weights cooperate permitting said manual adjustment oi the weights 5. The balance testing system set forth in claim 1, in which the machine set forth'in the claim revolves the rotor in a pair oi aligned bearings, the generator pivot being mounted'on one of said bearings.

6. The balance testing system set forth in clai 1, in which said meter is a vacuum-type voltmeter. 7. The balance testing system set forth in claim 1, in which said stroboscopic-lamp has a control amplifier operatively associated with it.

claim 1, in which onlyone of said two weights is adjustable toward and from the other companion weight.

9. Designed to coact with a machine of known type adapted to support and to rotate on its axis a rotor to be tested with freedom for lateral, substantially horiz ntal vibration of the rotor due to its unbalance during such rotation, a balance testing system incorporating the combination of a pair of piezoelectric crystal generators each including a vertical axis pivot having means operating its generator by turning of the pivot on its axis, each generator having means to mount its pivot on said machine in a manner to subject such pivot to said vibration of the rotating rotor, a longitudinal horizontal support fixed to each pivot and extending on opposite sides thereof and parallel to the geometrical axis of said rotor when such support is in its normal, neutral position, each such support having a pair of inertia weights adjustably mounted individually on said support on opposite sides of its pivot and each being manually adjustable longitudinally of its said support toward and from one another, each said generator having its electric circuit connected therewith, the two generatorshaving at least one electric meter for use in said circuits to which the voltage created by said generator is conducted and by which it is indicated, whereby said inertia weight means may be initially adjusted relatively to one another in one generator to cause zero reading or the electric meter for unbalance of the revolving rotor in one selected transverse correction-plane of the latter and may be preliminarily calibrated by the employment of known weight means applied to the rotor to show the amount of unbalance in the rotor in a second selected transverse correction-plane of the rotor, and the weight means of the other generator may be initially adjusted relatively to one another to cause zero reading of the electric meter for unbalance of the revolving rotor in the second correction-p1ane of the latter and may be preliminarily calibrated by the employment of known weight means applied to the rotor to show the amount of unbalance in the rotor in the first correction-plane of the rotor.

10, The balance testing system set forth in claim 1 which incorporates two such piezoelectric crystal generators each having all of the properties and characteristics presented in such claim but cooperative nevertheless with the two different correction-planes of the rotor.

11. The balance testing system presented in claim 9, in which the rotor in the machine is supplied with a graduated band around it with a stroboscope-lamp cooperating with said band, an electric circuit to supply said lamp with electric current, and means to connect said lamp circuit individually with each of the piezoelectric crystal 8. The balance testing system presented in v I 2.497 oso generators whereby to permit determination oi the angular position of the unbalance of the rotor in each of the two selected transverse correction-planes of the rotor. I

12. The balance testing system set forth in claim 1 which incorporates two such piezoelectric crystal generators each having all of the properties and characteristics presented in such claim but cooperative nevertheless with the two difierent correction-planes of the rotor, the rotor having in said machine a graduated band around it, with a stroboscopic-lamp cooperating with said band, an electric circuit to supply said lamp with electric current, and means to connect said lamp circuit individually with each piezoelectric crystal generator whereby to permit determination of the angular position of the unbalance of the rotor in said two selected transverse correctionplanes of the rotor.

13. A balance tester, designed to coact with a balance testing machine of known type adapted to support and to rotate a rotor to be tested with freedom for lateral vibration in a predetermined plane due to imbalance in the rotating rotor, said tester including a pivot member, means to mount said pivot member on said testing machine to vibrate in agreement with the vibration of the geometric axis of the rotor in said predetermined plane, the axis of said pivot member being substantially at right angles to said predetermined plane of vibration of the rotor, inertia weight means, means mounting said inertia weight means on said pivot member upon opposite sides of the axis thereof, and with manual adjustment of at least one of said weight means toward and from said pivot axis, the longitudinal axis of said means for mounting said inertia weight means extending substantially parallel with the rotor axis in its neutral position, and indicating means actuated by the oscillation of said pivot member occasioned by said weight means whereby said weight means may be preliminarily adjusted relative to one another tocause zero reading of said indicating means for unbalance in the rotating rotor in a selected transverse correction plane of the latter, and may be preliminarily calibrated to show the amount of unbalance of the rotor in another selected transverse correction plane through the rotor.

14. The combination in a balance tester set forth in claim 13 in which said weight means is two weights of different amounts.

15. The combination in a balance tester set forth in claim 13 in which said weight means is two weights, and in which said means mounting said weight means on said pivot member is a screw threaded rod permitting the specified adjustment.

16. The combination in a balance tester set forth in claim 13 in which said weight means is two weights of diiferent values and in which said means mounting said weight means on said pivot member is a screw threaded rod permitting the manual adjustment of said two weights.

1'7. The combination in a balance.tester set forth in claim 13 in which said indicating means includes an electric current operated indicator and a circuit for said indicator, and means for generating impulses of current in said circuit, said means being responsive to oscillation of said pivot member.

18. The combination in a balance tester set forth in claim 13 in which said indicating means includes an electric circuit containing a current operated indicator and a piezo electric crystal 12 generator connected to and operating said indicator and actuated by the oscillation of said pivot.

19. For use with a balance testing machine adapted to rotate a rotor in a pair of bearings with freedom for horizontal lateral vibration due to unbalance in the rotating rotor, balance testing means comprising the combination of a pivot member, means to mount said pivot member on one of said hearings to vibrate in agreement with the transverse vibration of said bearings, the axis of said pivot member being substantially at right angles to the plane of vibration of said bearings, inertia weight means, means mounting said weight means on said pivot member on opposite sides of its axis and with manual adjustment of at least one of said weight means toward and from the axis of said pivot member, the longitudinal axis of said means for mounting said inertia weight means extending substantially parallel with the rotor axis in its neutral position, and indicating means controlled by the oscillation of said pivot member occasioned by said weight means, whereby said weight means may be preliminarily adusted relative to said pivot member to cause zero reading of said indicating means for unbalance in the rotating rotor in a selected transverse correction plane of the latter other than the transverse plane of the bearing on which said pivot member is mounted, and may be preliminarily calibrated to show the amount of unbalance of the rotor in another selected transverse correction plane of the rotor other than that of the bearing on which said pivot member is mounted.

20. The balance testing means set forth in claim 19 in which said inertia weight means is two weights of unequal valuues and in which said indicating means includes an electrically operated indicator specifying the status of said rotor, an electric circuit for said indicator, and an electric current impulse generating means in said circuit actuated by the oscillation of said pivot member.

21. In a machine of the class described, a support comprising bearings for a rotor to be tested permitting the axis of the rotor to swing vibrationally in a horizontal plane of vibration and to carry the bearings with it, an extension on one of said bearings, an inertia device mounted on said extension and comprising a pivot member having a vertical axis, a horizontal rod carried on said pivot member and having its longitudinal axis substantially parallel to the axis of the rotor in its neutral position, inertia weights of different masses carried on the rod on opposite sides of the pivot member, at least one of said weights being adjustable as to distance from the pivot member, and means sensitive to oscillation of said weights and rod about said pivot axis for indicating unbalance of the rotor.

22. In a device of the class described, a pair of bearings for rotatably supporting the ends of one of a number of rotors to be subjected to analysis, said bearings being supported to permit vibrational swing of the ends of therotor in a single plane of vibration and to participate in said vibrational swing, a vibration detecting means associated with each bearing, each detecting means being connected with its associated bearing to participate in the vibrational swing of said bearing and comprising a pivot member disposed at right angles to the plane of vibration, a rod supported intermediate its ends on said pivot member, said rod being disposed with its longitudinal axis extending substantially parallel with the rotor axis in its neutral position, inertia weights mounted on said rod on opposite sides of the pivot member, an electric pickup device sensitive to the oscillation of the rod about its pivot, indicating means for indicating the degree of unbalance of a rotor in each of two transverse correction planes intersecting the rotor adjacent the corresponding bearings, indicating means for indicating the angular position of unbalanced forces in each of said correction planes, and an electric circuit and switches for connecting each of the electric pickups with each of said indicating means whereby the electric pickups govern the response of each of said indicating means.

IRA A. WEAVER.

CLYDE I-I. PHELPS.

aaraamcas crra'n The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,704,341 Rathbone Mar. 5, 1929 2,092,096 Swedlun'd Sept. 7, 1937 2,131,602 Thearle Sept. 27, 1938 2,293,371 Van De Grift Aug. 18, 1942 2,301,291 Kolesnik Nov. 10, 1942 3,363,303 Ehrgott et a1 Nov. 21, 1944 2,382,673 Sihvonen et a1 Aug. 14, 1945 2,382,843 Annis Aug. 14, 1945 

